Telephone-exchange system.



A. E. KEITH TELEPHONE EXCHANGE SYSTEM.

APPucATloN FILED 1AN.22. m01. RENEWED MAR. 2

A..E. KEITH.

TELEPHONE EXCHANGE SYSTEM.

APPLECATION FILED 1AN.22. i90?. LQSSAW.

RENEWEDMAR.20.1918.

Patented 0st. 29, 1918.

5 SHEETS-SHEET 2.

A. E. KHTH.

TELEPHONE EXCHANGE SYSTEM.

APPLxcATmN FILED JAN.22, 1907.

RENEWED MAR. 20. 1918.

aemed @et 29, 3.918.

5 SHEETS-SHEET 3- ad??? @s55/@ 652ML/ WLM A. KEITH.

TELEPHGNE EXCHANGE SYSTEM.

AYPLICATION FILED IAN. 22, 1907. RENEWEDMAR.20.19I8.

f 4 Q? llc. U.,

Patented 0%. 29, i918.

u WIM l 5 SHEETS-SHEET 4- Waff/265325( A. E. KEITH.

TELEPHONEEXCHANGE SYSTEM.

' APPLICATION m50 mm2. 1901. nENmvsnr.1An.2u.19|s. 33.9%@3941 3.

Patented Get. 29, 1918.

5 SHEETS-SHEET 5 @mf/M .A MCE.

ALEXANDER E. KEITH, OF CHICAGO, ILLINOIS, ASSIGNOR, BY MESNE ASSIGNMENTS, T0 AUTOMATIC ELECTRIC COMPANY, CORPORATION OF ILLINOIS.-

waterman-EXCHANGE SYSTEM.

Specification of Letters Patent.

Patented Oct.. 29), i918..

Application led January 22, 1907, Serial No. 353,488. Renewed March 20, 1918. Serial No. 223,675.

To all whom it may concern:

Be it known that l, ALEXANDER E. KEITH, a citizen of the United States of America, and resident of Chicago, Cook county, Illinois, have invented a certain new and useful In'iprovement in Telephone-Exchange Systems, of which the following is a specification.

My invention relates to automatic telephone exchange systemsin general, but more particularly to automatic systems which are operated on the district system principlesuch as systems involving a main central station and several outlying sub-central stations, with subscribers stations connected with the sub-central stations-, and especially to systems of this character employing a common battery or centralized source ofcurrent for both talking and switching purposes.

Generally stated the object of my invention is the provision of an improved and highly efficient telephone exchange system.

Special objects of my invention are the provision of means by which an attendant at the main orl central station can release the subscribers individual switches at the sub-central stations; the provision of an improved arrangement involving third or release trunk conductors between the main or central station-and the sub-central stations; the provision of means for indicating to the attendant at the central station the condition of the first-'selectors-that is to say, for giving a visual signal or indication whenever a first-selector is operated; the provision of means for indicating when a line is grounded and for automatically releasing the first-selectors by the fusing or blowing of the heat-coils; the provision of an arrangement by which the automatic releasing of the first-selectors in this manner will not operate to release the subscribers individual switches when the heat-coils are fused or blown by the grounding of the lines; the provision of an arrangement by which the restoration of the heat-coils by the attendant will automatically release the subscribers individual switches, providing the abnormal connection to ground has disappeared or been removed; the provision of improved individual switches for the subscribers telephone lines; and the provision of certain details andfeat-ures of construction and combinations tending to increase the general eiiiciency and serviceability of a, Vtelephone exchange system.

To the foregoing and other useful ends, my invention consists in matters hereinafter set forth and claimed.

In the accompanying drawings, Figures 1 and 2 taken together show diagrammatically an established connection between calling and called substations in a system embodying the principles of my invention. rThe system shown in said figures represents a district system the subscribers in which are arranged in groups, and the lines of each group terminating in a sub-central, while the main central office may be provided with trunking apparatus only.

Fig. 3 is a diagrammatic perspective view of o ne of the central office switches.

Figa is a diagram representing one of the switches individual to each subscribers line, together with the master switch for controlling all the line switches of the same group. In said figure the necessary connections between aline switch and a master switch are also shown. t,

F 1g. 5 is a plan view of one of the line switches.

n Fig. 6 is a sectional view of one of the line switch banks with the plunger or circuit cofitrolling arm in normal position.

Fig. 7 is a similar View showing the plungeror circuit-controlling arm in operative position.

Fig 8 is an elevation of the plunger or circuit-controlling arm of the line switch.

In Figs. l and 2 the calling substation is shown at A and the called substation at A. For the purposes of my invention the said substations may be considered as bein allotted to either the same or dierent su -exchanges; but in this ease it will be assumed.`

known. Comprised in said switching apparatus is a subscribers line switch@ which is of an improved and highly efficient type. The said switch C is a modified form of the switch disclosed in my prior application Serial No. 311,327, iled April 12, 1906, for telephone systems and apparatus. lt is designed to operate automatically (when the subscriber at the allotted substation sends in an impulse) to seize an idle trunk line leadinv to the next switch, preferably to ay firstse ector. The switch D with which the switch C is shown connected is a selector switch of the general type disclosed in United States Letters Patent No. 815,321, granted March 13, 1906, to Keith, Erickson and Erickson, and comprises certain new fea-I tures especially adapting it for supervisory work. The switch E is a master switch for controlling the line switch C and all other line switches of the same group. The connector switch F is a modified form of the connector disclosed in United States Letters Patent No. 815,176, granted March 13, 1906, to Keith, llrickson and Erickson, and is adapted for common battery work. The said line and selector and connector switches are adapted to be operated from the calling substation by ground impulses derived from the grounded terminal G ot the battery B. The central exchange is further provided with a central source of ringing current H and a source of busy-signaling current L The switch J is allotted to the called substation A and is, ot course, similar to the switch C. The substations A and A may be of any suitable type. Ilhe substation A comprises a receiver 2, switch-hook 3, induction-coil 4t which consists of the primary winding 5 and secondary'winding 6, transmitter 7, condenser 8, and the ringer 9. ln addition to the above-mentioned parts there is provided an impulse wheel 10 which has the usual vertical impulse teeth 11 that are adapted to operate the vertical impulse spring 12. 'lhe impulse wheel carries the rotary impulse tooth 13 which operates the rotary impulse spring 14. The switch-hook has radiating :from its body a number of cam arms 15, 16

' `and 17, and is pivotally secured to the keyboard (not shown) by the screw 18 about which it moves when the receiver is removed. rlhe movement is produced by a spring (not shown), and the switch-hook is pushed up :tor the purpose ot changing certain circuit connections to be disclosed. 'llhe cam arm 15 controls the so-called locking armi 19 that normally rests in the position f shown at substation A. Atter the switchhook has reached its uppermost position the locking arm 19 occupies the position shown at substation A. The coperating ground springs 20 and 21 engage, thus placing the ground post 22 in contact with the substation ground G', whereby, when the subscriber releases the nasa-ria dial after rotating it as described, the vertical impulse teeth 11 will cause the vertical impulse spring 12 to come into contact with the ground post 22, and immediately following, the rotary impulse tooth 13 causes the rotary impulse spring 14 to come 'into con- .tact with the same ground post 22. When the switch-hook is down the cam arm 17 maintains a contact between the springs 23 and 21, thereby bridging the ringer 9 across the line. The springs 2 6 and 27 are then disengaged, dand the primary circuit, including the winding 5 in series with the transmitter 7, is interrupted by the separation of the springs26 and 27. rll`he signaling device whereby a subscriber may signal another after a connection has been established comprises a push-button 28 and a spring 29, which latter normally engages the contact point 30; but when the push-button 28 is pressed the spring 29 leaves the contact point 30l and engages the contact point 31' which is connected with the substation ground G. Means whereby the subscriber may release the central station apparatus brought into service comprises three springs 32, 33 and 34, known as the release springs, so controlled by the cam arm 16 that when the switch-hook descends the three release springs are momentarily brought into contact, thereby grounding both the subscribers4 line conductors simultaneously.. ln addition, the substation A is provided with a fourth cam 35 which is suitably insulated 'from the switch-hook 3. Said cam is adapted to momentarily engage the spring 36 when the receiver 2 is removed and the switchhook rises. This momentary engagement when the receiver is removed produces a preliminary impulse, whereby the line switch C is operated. The lswitch D (shown in Figs. 1 and 3) embodies, among other details, the following well-known devices and circuits: a switch-shaft 38 which carries the vertical and rotary wipers 39 and A0, respectively, and the private wiper 11. rlFhe saidwipers are adapted to engage the banks 'llt and L. rl`he side switch ll/l is well known and comprises the side switch wipers 42, t3, lt and 15 which may be designated as verticahrotary and private side switch wipers and the rotary magnet side switch wiper, respectively. 'llhe side switch is under the control ot the private magnet L16. rLhrough the medium or the vertical line relay L17, and while the side switch is in first position, the subscriber controls the vertical magnet 48, `which latter operates to raise the switch-shaft and shaft wi ers 39, 4:0 and A1 vertically. By

Ameairis o the rotary line relay A9, and while the side switch is in first position, the subscriber' controls'the private magnet A6 and, therefore, `the side switch. While the side rasante wipers in a rotary or circular direction, is energized. The vertical and rotary line relays 47 and 49, acting conjointly, provide means whereby the subscriberv controls the release magnet 51 while the side switch is in rst or second position. vAfter the side switch passes to third position, then, since the first-selector is of the trunk-release type, the said switch is controlled from the neXt switch with which a connection has been established through the private-wiper 41 and by means of the back-release relay 52. lin addition, the lamp-relay 53 is provided for closing a circuit through the signal lamp 54 whenthe first-selector is seized by a line or subscribers individual switch. Through the heat-coil 55 the operating relays and magnets receive battery current. Also, the signal lamp 56 is provided for indicating to the central oliice attendant that'a heat-coil of the selector group including selector D has blown. The lamps 56 and 562 are corresponding group lamps of other first-'selector groups similar to the group including the switch D. The relay 57 is common to the group of lamps 56, 56', 562, etc.; hence when any lamp 0f the said group glows, the energizing current passes through the relay 57, which in turn operates to give an audible signal. Furthermore, the lamp 58 is, like the lamp 56, allotted to a group of switches. One terminal of the said lamp 58 is connected with the third contact point of the wiper of the selector D. The corresponding wipers 45 and 452 are of other first-selectors of the sameygroup as the selector D. rlhe functions of these signal lamps will be more fully explained hereinafter in connection with the calling operation. rlhe line or individual switch shown in F ig. 5 is an irnprovement upon the line orsubscribers individual switch shown in my said previous application, and is built about a metallic base or frame 59 and comprises a plunger 60 and plunger arm 61. lt is also equipped with a bridge-cut-od relay 62, a trip magnet 63 and switch-release magnet 64. A .section of the metal from the central portion of the frame is removed to make the structure as light as possible, while another section of the portion is turned up at a right angle to the base of the frame to forma lug or flange 65 upon which the said switch-release magnet is mounted. Said flange has stamped through it a couple of circular-holes through vwhich the ends of the cores 66 are passed to maintain the coils of the said release magnet parallel with the base of the frame. They are retained in this position by a tlshaped locking collar 67 between 'the faces of which the magnet-supporting flange en tends. Said collar has four openings (two on each of the parallel faces) arranged to forni. two tandem sets through which the cores of the swi.tch-re.lease magnets also pass, as shown. After the magnets are inserted in position they are then tightened in place by a shearing action produced upon the said cores of the switclrrelease magnets, between the tiange and the capping collar, by' means of a screw 68 that passes through a threaded portion on the said collar, the end of which screw is forced onto the upper edge of the magnet-supporting iange 65. rlhe said switch-releaseV magnet is provided with an armature 69 that is pivoted on a pin 70 which Yrises from thebase of therswitch. The said armature carries pivotally secured on its end a second armature 71 that is controlled by the trip magnet 63. rlhe pin 75 about which the/armature 71 oscillates is carried on the end of the armature 69. rlhe plunger 60 is pivot-ally secured by the pin 76 to the plunger arm 61, which latter is in turn pivoted to a pin 77 that rises from the switchframe 59. The lug 78 is stamped out of the side of the frame 59 and serves as a stop or rest for the armature 69. The trip magnet 63 is mounted upon the frame 59 in the same manner as the release magnet 64. Upon the armature 71 is secured the catch spring 79 which is adapted to enga ge the end of the plunger arm 61. The general operation of the switch is as follows: First the trip magnet 63 is energized by a preliminary impulse, and the armature 71 is attracted against the magnet cores. When the armature 7l is attracted to the right (Fig. 5), the. catch 79 slides from the end 80 of the plunger arm 6l, and the said plunger arm 6l, owing' to the tension of the spring if?, moves about the pin 77 and thrusts the plunger 60 intoy the bank Q (shown in Fig. 4); and when the trip magnet lagain denergizes, the trip armature '71 falls against the end of the plunger arm 6l. The switch is restored when the release magnet 64 becomes energized, where by the armature 69 is attracted, and accord ingly the trip armature 71 is moved upwardly until the catch 79 again slides -over the end 80; then when the release magnet 64- becomes denergized th-e armature 69 returns to normal position and remains at against the stop 7 8. Furthermore. since the plunger arm 61 is now in engagement with l. c

the armature 71, the said plunger arm is also moved about the pin 77, whereby the plunger 60 is removed from the bank (d, to the position shown in Fig. Als-o, since the plunger' shaft has advanced one step., the

hub 73 of the plunger 66 cornes to in the position shown by the dotted lines in i against the plungershaft 94; and the plunger shaft advances each time an trunk is seit/fed, the plunger 66 is vanced hut remains in this po the trunk terminal l disengaged., since the e gagenient with the L all. of the trunk lOll l l. fl

seized, and the plunger shaft-.again passes to the position it occupied when the plunger 60 seized the terminal Q, the 4plunger 60 retu`rns into engagement with the said plunger shaft. In the meantime, if the line switch C is again operatcdg'the plunger 60 again engages the same terminal Q. In Fig. 8 is shown a side elevation of the plunger G0, to which is secured the roller bushing 80 by means of the pin 81. The bridge-cutoft" relay 62 is provided with the springs 82, 83, 84 and 85, the former two (82 and 83) for controlling the energizing circuit of the trip magnet 63, and the latter (84 and 85), when in engagement, .connecting the subscribers vertical line conductor with the vertical normal conductor. When the cut-0E relay 62 is denergized'the springs 82, 83 and 84 engage, and the springs 84 and 85 disengage. Thefengagement of the former set (82, 88 and 84) connects both the subscribers? line conductors with the battery through the trip magnet 63. This provision is made in order to keep both sides of the line balanced. The said line switch is provided with a bank of terminals (Fig. 4), usually ten in number, only one of which is shown at Q. As shown in Fig. 4, the said terminal Q is rotated ninety degrees Jfrom its true position with respect to the swing of the plunger 60, and the bushing 80 is correspondingly turned, all for the purpose of vmaking the illustration clearer. rlhe true relative positions of the plunger and banks is shown in Figs. 6 and 7. The terminal Q comprises the springs 86 and 87, 88 and 89, 90 and 91, and 92 and 93. The said springs are normally disconnected from each other, but are driven into contact in the abovementioned order when the plunger 60 operates. Normally, the plunger 60 is, however, retained out of engagement with the line switch bank and in engagement with the plunger-controlling shaft 94, which latter iS operated by the master switch E. rlhe master switch l may be of any suitable or'approved type, and is provided for operating the plunger shaft 94 and for controlling certain circuits that will be disclosed hereinafter. 1t comprises the following details: a

motor magnet 95 for operating the ratchet wheel 96. which latter is designed for operating the plunger shaft 94; also a dien ential relay 97 for controlling the energizing circuit of the motor magnet 95. 'llhe said master switch also has a bank O comprising a plurality of individual contact segments a and a metallic segment 98, as shown in Fig. 4. The wiper 99 is adapted to remain in constant engagement with the bank 0, and to at all times maintain some one of the seglments a in electric connection with the common segment 98. rThe wiper 99 is operated in a stepbystep manner by the ratchet wheel 96, through the medium of a cam member 100 rigidly secured to the said wiper 99 and adapted to successively engage the pins 101, 102, 103 and 104 upon the said ratchet wheel 96. The motor magnet 95 is\ provided with an armature 105 upon the end of which there is suitably securedua pawl 106. Each time that the said magnet is energized the pawl 106 engages the ratchet wheel 96, advancing the latterone step. It will be noticed, therefore', that as the ratchet wheel 96 advances in a counterclockwise direction the wiper 99 advances step-by-step from right to leftgand when the pin 101, for instance, clears the cam 100 the retracting spring 107 restores the wiper 99 to its first position at the right of the bank 0 and in engagement with the first segment 108. The said motor magnet 95 is provided with a couple 'of interrupter springs 109 and 110 that are included in the energizing circuit of the said motor magnet, which energizing circuit also` comprises the springs 111 and 112 controlled by the differential relay 97. Therefore, whenever the dierential relay 97 is energized the springs 111 and 112 are pressed into contact, and the motor magnet 95 operates step-by-step as long as the dierential relay 97 remains energized. Further, it iS assumed that the terminal Q of the line switch C' is the first terminal of the line switch bank. rllhe plunger 60, while in normal engagement with the shaft 94, is retained in front of said terminal by the plunger shaft 94 whenever the master switch wiper 99 is in engagement with the bank segment 108; but as the motor magnet 95 advances the wiper 99 onto the second segmentI 113, the said plunger and all idle plungers similarly' engaging the shaft 94 are carried opposite the next terminal of the line switch bank. It should be noted that in each switch all of the springs 90 are permanently connected and may be made of one com-mon piece. The springs 93, however, are individual-that is, there is one separate and distinct spring for every bank set U, there being ten in the bank. The springs 88, 86, 92 and 91, like the springs 90, are also common, and the springs 87 and 89, like the springs 93, are individual. For every bank terminal Q there is a trunk line of three conductors 114, 115 and 116 leading to a selector; andv there is also a normal trunk line comprising the ,conductors 117, 118 and 119 leading to the connector banks. The sub scribers line conductors 120 and 121 termi. nate in the springs 86 and 88 which, as has" been stated, are common springs. When the subscriber operates the line switch C andthe plunger 60 engages the terminal Q, the sub1` scribers line conductors 120 and 121 are eX- tended to the vertical and rotary trunk conductors 114 and 115 and thence to the switch D. The connector switch F maybe of any suitableor approved type.y The mechanical rasante et details et' the rst-selector and connector, as is Well known, are very much the same, although there is some material (lider-ence in .the circuits. 'lhe connector switch F is an improvement upon the connector disclosed in said connector patent and in application Serial No. 294,663, tiled January l, 1906, by '.l. G. Martin for improvement in common battery automatic telephone systems. The vertical and rotary line relays 122 and 123, respectively, receive battery current through the windings 124i and 125 or the diiilerential relay 126. 'lihe vertical land rotary magnets 12T and 128 are directly under the control ot' the vertical line relay 122. 'lllie private magnet 129 is controlled by the rotary line relay 123, and said private magnet 129 in *turn operates to release the side switch wipers 130, 131, 132 and 133 from Erst to second position, and from second to third position. The release magnet 131, when energized, operates to restore the side switch and switch-shaft Wipers 135, 136 and 131,. 'lihe ringer relay 138 peri'orms the usual function oi bridging the ringer generator 'across the line et the called subscriber, While through the windings 139 and 1410 of the relay 111 the calledsubstation receives battery current :tor talking purposes. When the relay 141 energizes, the calling substation is then provided with battery current tor talking purposes.

El. clearer understanding of the operation of my improved system may be obtained by considering its operation when one subscriber calls another. Assume, for example,

that the subscriber at substation A desires y to call the subscriber at substation A. ,to `which is allotted the line 9:220, 'lo call the number 220 the subscriber at substation it operates the calling device once for each digit, in the welllrnown manner.. 'llhe preliminary impulse tor operating the line or individual switch C occurs when the calling subscriber removes the receiver 2 from the switch-hookl 3, whereby the hook in risin permits the cam to engage the 'ground spring 36. As a result the trip magnet 63 of theline switch C is ener ized by a dow ol current from ground to the spring 36, thence to the switch-hook cam 35 and to the rotary line conductor 121, conductor 142, cut-ott relay springs 83 and 62 to the trip magnet 63, thence through said trip magnet to the conductor 143, motor magnet springs 110 and 109, Winding ot the motor magnet 95 to the battery lead lett,

thence through battery B to ground G.- 131s soon as the trip magnet 63 energiaes, the

larniature l1 is then attracted and the lun ger 69 is liberated and thrust into the anh terminal Q by the spring 72'. The motor magnet 95, upon energizing, attracts its armature 195, whereby the paal' 106 engages the ratchet `Wheel 96 and rotates theY said terminal Q) to the contact point 113, which latter corresponds to the terminal before `which the idle plungers are non7 resting. At the instant that the said plunger 60 enters the said bank position Q the followin springs arelpressed into contact: 88 and 89, 90 and 91, 92 and 93, and 86 and 67. rlhe engagement of the springs 90 and 91 establishes a circuit from ground G2 by Way of the normal conductor 119 to the connector private bank contacts corresponding to the line that terminates in the line switch C,

whereby a guarding potential is set up to prevent any subscriber from calling the said line after the calling subscriber at substation A removes his receiver preparatory to making a call, as explained. rlhe circuit over which the said guarding potential is established extends from ground G2 through the banlr springs 90 and 91 to the private normal conductor 119, thence to the connector private banks. The closure otconnee tion between the springs 92 and 93 also establishes a guarding potential at the master switch bank Contact 106 over the following circuit: trom battery B to the battery lead 114-, thence tothe release magnet 61, and through the said'magnet and springs 92 and 93 over the conductor 145 to the said contact point 108. 1t will be understood that the bank terminal Q, being the lirst bank terminal ot the line switch, corresponds to the irst segment 10601 the master switch bank t). r1`he said guarding potential protects the seized trunk lines 11d, 115 and 116 trom being seized by other lungers. Suppose that the master sWitc has operated and carried the wiper 99 to the last contact point 1416. New, when the motor magnet 95 operates tor the next step, the Wiper 99 engages the Contact point 109, upon which there is a guarding potential. hn ener,iz ing circuit is established through the itterential relay 97, Which in turn operates to close an energizing circuit through the motor magnet 9.5. rlhe current through the said relay 97 doive from the said Contact 109 through the Wiper 99 to the common segtuent 99, thence over the conductor 1417, through the Winding 118 of the diilerential relay 97 to ground G3. lWhen the difierential relay 97 attracts 4its armature the dititerential relay springs 111 and 11.2 are pressed into contact, thereby closing an energizing circuit for the motor magnet 95 from ground G4 through the said springs 111 and 112 to the motor magnet springs -110 and 109, thence through the said magnet 95 to the battery lead 144, and through battery B to ground G. The motor magnet then operates to rotate the ratchet `wheel 96 one step for advancing the plunger shaft 94 one step, and also the master switch bank wiper 99 one step, into engagement with the second segment. 113. The plunger shaft 94 when thus advanced one step carries all idle plungers that are in engagement with the said shaft opposite the next bank terminal, as previously explained. 1f there should be a guarding potential at the bank segment 113 of the master switch the differential relay 97 will remain energized after the motor magnet armature 105 returns to normal position and again closes connection between the springs 109 and 110. As a result the motor magnet 95 is again operated, whereby the plunger-shaft 94 and the master switch wiper 99 are advanced another step. r1`his process continues as long as the wiper 99 continues to find segments with guarding potentials. As soon as an idle segment is found, however, the energizing circuit through the diderential relay 97 is broken, at which time the said relay in turn breaks the energizing circuit for the motor Vmagnet 95 until the next subscriber makes a call. Furthermore, the closing in contact of the springs 92 and 93 completes an energizing circuit through the lamp relay 53 of the first-selector D, said circuit eX- tending from ground G to the side switch Wiper,45, contact point 154, conductor 155, through the lamp relay 53, private trunk conductor 116, bank springs 93 and 92, through the release magnet '64 to the battery lead 144, thence through battery B to ground G. Although the trip magnet 64 is included in this clrcuit, the vsaid magnet does not energize, since the relay 53 is wound to a high resistance. The lamp relay'53, upon energizing, closes the springs 156 and 157 in contact, whereby a circuit is closed through the signal lamp 54 extendin from ground G7 through the springs '157i and 156, through the lamp 54 to the conductor 158, heat-coil springs 159 and 16.0 to the battery lead 144, thence through battery B and to ground G. rllhe glowing of this lamp indicates to the exchange attendant that its allotted first-selector D has been seized by a. line switch. When the side switch wiper passes to second position the lamp relay 53 denergizes and the signal disappears. The closure o1 connection between the springs 86 and 87 extends the calling sbscribers vertical line conductor 120 to the vertical trunk conductor 114 and to the side switch wiper 42 ot the rst-seinea-aia lector D. The closure of connection betweenthe springs 88 and 89 in a similar manner extends the subscribers rotary line conductor 121 to the rotary trunk conductor\115 and to the side switch wiper 43 of the selector D. The subscriber has thus established connection with the selector D and is ready to begin operating his calling device for the first digit. The first digit being 2, the subscriber operates his dial accordingly, grounding the vertical line conductor 120 each time that the spring 12 is pressed onto the ground post 22. As a result the vertical line relay 47 of the rstselector D is energized by a flow of current from the substation ground G through the springs 20 and 21 to the ground post 22, thence through the spring 12 to the vertical line conductor 120, line switch bank springs 86 and 87, vertical trunk conductor 114, side switch wiper 42 of the selector D, contact point 161, vertical line relay 47, conductor 158, through the heat-coil springs 159 and 160 to the battery lead 144, thence through battery B and to ground G. Each time that the vertical line relay 47 energizes, the line relay spring 162 is pressed onto the ground post 163. r1he vertical magnet 48 is thereby energized and the wipers 39,49 and 41 of 'the selector D are yraised to the second bank level opposite the rst contact of said level. The energizing circuit for the said vertical magnet 48 extends from ground G5 through the springs 163 and 162. private springs 164 and 165 to the vertical magnet 48, conductor 158, through the heat-coil springs 159 and 160, thence to the battery lead 144, and through battery B to ground G. The spring 14 is then pressed onto the gr'o'ind post 22, grounding the rotary line conductor 121 and energizing, therefore, the rotary line relay 49 ofthe selector D. rllhe energizing current passes from ground G to the rotary line conductor 121, through the line switch bank springs 88 and 89, rotary trunk conductor 115, side switch wiper 43 of the selector D, contact point 166` to the rotary line relay 49, conductor 158, thence through the heat-coil springs 159 and 160 to the battery lead 144, and through battery B nto ground G. The rotary line relay, upon wipers 44 and 45 to engage the contact.

points 167 and 168, respectively. 'lhe closure of connection between the side switch wiper 45 and the contact point 168 sets up an energizing circuit for the rotary magnet 50 from ground Gr through the side switch wiper 45, to the contact point 168, conductor 169, interrupter springs 170, rotary magnet 50, conductor 1.58, through the heat-coil springs 159 and 160 to the battery lead 144, thence through battery B to ground G. The said rotary magnet 50 then operates to rotate the wipers 39, 40 and 41 of the selector' D into engagement witlra trunk line leading to some idle connector switch, and in the particular case under consideration t0 the connector switch F. 1f the wipers have to pass over busy trunk lines, as soon as the private wiper 41 engages a grounded contact point the private magnet 46 again energizes, locking the side switch in second position. rl`he energizing circuit :tor said private magnet extends from the grounded terminal (if bf battery 'B through an occupying switch (not shown) to the private wiper 41, thence over the conductor 171 and through the back-release relay 52 to the side switch wiper 44, Contact point 167, private magnet 46, thence through said magnet to the conductor 158, through the `heat-coil springs 159 and 160 to the battery lead 144, and through battery B to ground G. 'l` he private magnet 46, upon thus becoming energized, locks the grounded side switchgwiper 45 1n engagement with the contact point 168, whereby the rotary magnet 50 is energized step-by-step until the wipers are carried beyond the last busy trunk line. .At the instant that the private wiper leaves the last busy contact point, the energizing circuit through the private magnet 46 is destroyed, and as a result the selector side switch passes to third position. lf however, there are no' busy trunk lines, the rotary magnet 50 releases the side switch to third position as soon as the wipers are carried into engagement with the first trunk line. As soon as the side switch passes to third position, as stated, the snbscribers line conductors 120 and 121 are extended to the conductors 172 and 173, which in this case, it is assumed, lead to the connector switch F. rllhe extension of the line occurs, ofv course, as soon as the side switch wipers 42 and 43 engage the contact points 174 and 175, respectively. Not only is the subscribers line thus extended, but a guarding potential is also established at the private wiper 41 when the side switch wiper 44 passes onto the grounded Contact point 176 for protecting the seized trunk line from interference by other calling subscribers. This guarding potential is established from ground (Si8 to the contact point 176, thence through the side switch wiper 44, through the back-release relay 52, conductor 171 to the private Wiper 41. 1t will be necessary, of course, that the energizing circuit for the rotary magnet 5() (to which reference has already been made) be destroyed when the idle trunk line is seized. This occurs when the grounded side switch wiper 45 leaves the contact point 168. Also, when the grounded side switch wiper 45 passes to third position in contact with the point 177, an energizing circuit is established through the group lamp 58 extending from ground G through the side switch wiper 45, contact point 177, conductor 178, through the lamp 58 to tho battery lead 144, thence through battery B -and to ground (i. The glowing ot' the said lamp indicates to the exchange attendant that some selector of the group to which lector D belongs has operated and seized a trunk line leading to the connector switches. The lamp `58 continues to glow as long as any ot' its group selector side switch wipers 45, 45', 45, etc., (which latter two it is assumed belong to other switches) remain in third position. The second digit ot the number called being 2, the calling subscriber operates his dial again accordingly, as a result grounding the vertical line conductor 120, when the spring 12 meets` the ground post The vertical line relay 122 of the connector switch F is, therefore, energized twice by a tiow of current from the substation ground G to the vertical line conductor 120, thence through the line switch bank springs 86 and 87 to the vertical trunlt conductor 114, thence to the side switch wiper 42 of the selector D, contact point 174, vertical line wiper 39, vertical trunk eonductor172, vertical line relay 122, winding 124 of the differential relay 126 to the battery lead 144, thence through batterv li to ground G. This circuit, then, comprisesl the winding 124 of the dtferential relay 126, so that the said ditl'erential relay energizes sir multaneously with the vertical line relay 122; but the said energization produces no effect at this stage. The vertical line relay 122, uponv energizing, presses the line relay spring 179 into engagement with the ground spring 180. as a result operating the vertical magnet 127 twice by the establishn'ient ot a circuit from 'ground G9, through the springs 180 and 179, through the private magnet springs 181 and 182 to the side switch wiper 133,thence through the contact point 188 and 'vertical magnet 127 to the battery lead 144, thence through battery B and to ground (i. As is well known, the vertical magnet 127 then operates to raise the switclrshatt wipers 135, 136 and 137 of the connector F to the second bank level. The connector having been thus operated, then when the rotary impulse spring 14 engages the ground post 22 the rotary line conductor 121 is grounded once, energizing the connector rotary line relay 123 over the following circuit: from ground G at the substation i to the rotary line conductor 121, through the line switch l.

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bank springs 88 and 89 to the rotary trunk conductor 115, thence to the side switch wiper 43 of the selector D, contact point 175, rotary line Wiper l10, rotary trunk conductor 173 to the rotary line relay 123, thence through the ditlerential relay winding 125, back-bridge relay springs 181 and 185 to the battery lead 141, thence through battery B` and to ground G. `r1he differential relay 126 again energzes, but still to no effect. The rotary line relay 123, however, presses the line relay spring 186 onto the ground spring 180, as a result energizing the private magnet 129. 'The circuit established extends from ground G to the springs 180 and 186, to the private magnet 129, backbridge relay springs 181 and 185 to the battery lead 141, and through battery B to ground G. The private magnet, upon energizing and denergizing permits the connector side switch to pass to second position, and, among other results, shifts the side switch wiper 133 into engagement with the Contact point 187 The rotary magnet 128 .is thus substituted for the vertical magnet 127, as tar as the control thereof by the vertical line relay 122 is concerned. The third digit of the desired number being naught, the calling subscriber operates his dial to ground the vertical line conductor 120 ten times. Ars a result the vertical line relay 122 of the connector F is energized ten times, and the line relay springs 179 and 180- operated accordingly. 'llhe rotary magnet 128 is energized each time overacircuit extending froni ground G through the line relay springs 180 and 179, and through the private springs 1.81 and 182 to the side switch wiper 133, thence through the contact point 187 and the rotary magnet 128 to the battery lead 141, thence through battery B and to ground Gr. '111e said rotary magnet then operates to rotate the` shaft wipers 135, 136 and 137 step-bysteponto the tenth contact of thev second Alevel of the connector bank from which terminal leads a trunk line that entends to the called subscri'bers line :#:220 r1`he -rotary line conductor 121 is again grounded once, energizing the rotary line relay 123 of the connector F over a circuit that has been pointed out. tarte line relay then presses the springs 180 and' 186 into Contact, as previously explained, with the result that the private magnet 129 is again energized. llnergizing the rotary line relay 123 at this time produces one o1 two results, namely the release of the connector' side .switch from second to third position and establishing the desired connection, or the busy-release of the connector switch it the desired line is .busy.

r1`he former result will tiret be considered,`

namely the release ont the connector side switch from second to third position. 'llhe release o1 the side switch occurs when the Called line.

rlhe said roprivate magnet 139 energizes and denergizes as heretofore explained. At the instant that the said side switch passes to third position, the connector side switch wipers 130 and 131 having engaged the contact points 187 ,and 188 extend the calling subscriber-s line conductors into connection with the normal conductors 189 and 190 which lead to the Furthermore, when the side switch passes to third position a guarding 'potential is established for protecting the called line. This potential extends from ground G10 to the contactv point 207, side switch wiper 132 to the shaft lwiper 137, which latter engages the private contact 'of the called line. The said guarding potential also closes an energizing circuit through the cut-od relay 149 of the line switch J, thereby removing the short-circuit from across the vertical and rotary line conductors of the called substation at the line switch J,

'and connecting Athe vertical normal cohroo nector vertical line relay 122 and also the differential relay 126, over circuits that have been pointed out. rll`he operation 4et said relays 122 and 126 causes the energization'of the connector ringer relay 138 over the, following circuit: from ground G9 at the connector through the line relay springs 180 i and 179, private springs 181 and 182 andu side switch wiper 133 to the contact point 191, to the ringer relay 138, thence through the diterential relay springs 192 and 193 to the battery lead 1411 andthrough battery B to ground G. f course', since the v.diderential relay 126 is energized, and said springs 192 and 193 are in contact, the en; ergization of said ringer relay 138 bridges the ringer generator 11 across the normal conductors 189 and 190, whereby ringing current is projected over the normal line conductors 189 and 190 to the substation :#220 for operating the ringer at the saidl substation. The path o1 the rin 'ng current. is as follows: from the ringer ienerator 1-1 through the ringer relay springs 191 and 195, and through the side switch'wiper 130,

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contact point 187, Wiper to the vertical normal conductor 189, thence to the vertical line conductor 196, condenser 197, through the ringer 198at substation #220, springs 199 and 200 to the rotary line conductor 201, thence over the rotary noimal conductor 190, wiper 136, contact point 188, side switch wiper 131, ringer relay springs 202 and 203'- to the ringer generator H again. The sub? scriber at substation #220, upon respond-` ing, bridges his transmitter 204 and primary winding 205 of the induction-coil 206 across his line conductors 196 and 201. When the-V connector side switch passes to third position, as explained in the foregoing, the battery B is bridged across the line'for' furnishing talking current thereto, and when themal conductor 190, rotary line conductor'V 201, primary winding 205, transmitter 204, and through the springs 209, and 210 to the vertical line conductor 196, springs 15,0 and `151, thence overthe vertical normal conductor 189, vertical line wiper 135, contact oint 187, side switchl wiper 130, vertical ackbridge winding 139, through the springs 152 and 193 to the battery lead 144, and through battery B to ground G. The back-bridge relay 141, upon energizati'on, presses the springs 184'and 209 into engagement, thus connecting battery-,B across the line of the calling subscriber as follows: from ground G10, side switch wiper 132, through the back bridge relay springs 209 and 184, winding 125 of the di'erential relay 126, rotary line relay 123 tothe rotary trunk conductor 173,

and through the selector D and line switch C to the rotary line conductor 121, primar winding '5, transmitter 7, springs 26 and 2 to the vertical line` conductor 120, thence through the vertical linerelay 122 of the connector F, and through the winding 124 of the differential relay 126 to the battery lead 144, thence through battery B'to ground G. The two substations A and A being thus supplied with battery current, communication may be carried on over the conductors shown by the heavy lines in Figs. 1 and 2. The release of the central oiiice switching apparatus occurs when the calling subscriber hangs up his receiver andfgrounds his ver tical and rotary line conductors 120 and 121 simultaneously, thereby producing a release of the switches through the `medium of which the connection has been established; As the switch-hook 3 descends the release springs 32, 33 and 34 are pressed into contact, whereby the vertical and rotary line relays 122 and 123 of the 'connector F are energizedtogether with the dierential relay 126, in the following manner: The primary result of grounding the rotary line conductor 121 is to unbalance the dierential relay 126 by shunting or shortcircuiting the winding 125 between the ground G at the substation A and ground G10 at the connector F. The shunting or short-circuiting branch may be traced from the substation ground G to the ground springs 20 and 21,-

thence to the release springs 32 and 33, to

the rotary line conductor 121, line switch' bank springs 88 and 89, irst-selector side switch wiper 43, rotary wiper 40, trunk conductor 173, rotary line relay 123, winding 125 of the differential relay 126, back-bridge relay springs 184 and 209 to the side switch wiper 132 and to ground G10. The dierential relay immediately energizes by the flow of current through the winding 124 by' reason of the ground connection to the vertical line conductor 120. rThe magnetizing curlrent fiows from substation ground G to the ground release spring 32, thence through the release springs 33 and 34 to the vertical line conductor 120, line switch bank springs 86 and 87, connector vertical line relay '122, winding 124 of the diierential relay 126 to the battery lead 144, thence through battery B to ground G. The differential relay 126, upon energizing, separates the spring 152 from the spring 193, and carries the s rings 193 and 192 into engagement. `'lFhe ormer of said springs, namely the springs 152 and 193, as already explained, are comprised in the energizing circuit of the back-bridge relay 141, so that as soon as the said springs separate, the said relay 141 denergizes, w ereby the spring l184 leaves the ground spring 209 and returns into engagement with the non-grounded battery\spring 185. The effect of this last operation is to remove the shunt from the differential relay winding 125 in series with 'the rotary line relay 123, asalready described, establishing a circuit through said relay and winding, whereby a current-How is set up ina reverse direction,-

further strengthening the differential relay 126 and renergizing the rotary Aline relay 123. Under these conditions the line relays 122 and 123 are energized, whereby the trunk-release springs 212v and 213 "are pressed into contact while ,the diierential relay springs 193 and 192 are in engagement, with the result that an energizing circuit is established through the release magnet 134 of the connector Fin series with the backrelease relay 52 of the selector D. The release magnet 134 of the connector, upon energizing, restores the side switch and the switch-shaft to normal position in the wellknown manner, 'at which time the line4 and private wipers 135, 136 and 137 are, of course, disconnected from the normal conductors 189, 190 and 214. The energizing of the back-release relay 52 carries the backrelease relay springs 215 and 216 into engagement, as a result energizing the release magnet 51 from ground G11 through the sa1d springs 216 and 215, through the release magnet 51, heat-cgil springs 159 and 160 to the battery lead 144, thence through battery B to ground Gr. The selector release magnet, upon energizing, draws its armature into position to release the switch when the release springs at the substation disengage, as described in connection' with the said selector patent. 1n thesame manner that the connectorcontrols the energizationof the release magnet 51 of the selector D, the said release magnet 51 in turn controls the energizing circuit of the release magnet 64 of the switch C. rllhis is done through the medium o1 the springs 217 and 218 which are under the control of the armature of the release magnet 51 of the selector D. Therefore, when the armature of the release magnet 51 is attracted, an energizing circuit is set up through the release ma net 64 of the switch C when the sprin s 21 and 218 are brought into contact, which energizing circuit extends from ground G12 through the springs 218 and 217, conductor 116, bank springs 93 and 92, through the release magnet 64 to the battery lead 144, and through battery B to ground G. When the release magnet 64 energizes, the armature 69 is attracted, whereby the armature 71 ot the trip magnet'63 is raised and the catch 79 engages the terminal 80 of the plunger` arm 61, remaining thus in readiness to restore the line vswitch when the release magnet 64 denergizes'suiliciently. As soon as the substation release springs 32,33 and 34 separate, the energizing circuits of the rotary and' vertical line relays 122 and 123 o1 the connector F are destroyed. 'As a result, the energizing circuit through the release magnet 134 and the back-release relay 52 is broken. The deenergization of the back-release relay 52 in turn causes the denergization of the selector release magnet, with the result already stated, causing the denergization of the release magnet 64 of the line switch C. When the release magnet 64 of the said line switch denergizes, the retracting spring 72, through the medium of the armatures b9 and 71, withdraws the plunger trom its o perated condition into normal engagement with the plunger shaft 94, as a result destroying, o1 course, the energizing circuit of the cut-od1 relay 62, removing the guarding potential from -the master switch bank 0 ,d

the :torce by which the same plunger is restored. A description of how this occurs is as follows: When the plunger 60 is in normal position the armature 69 of the release magnet 64 is resting against the stop 78 and cannot, therefore, be further lowered.. lFurthermore, the spring 72 is maintained under tens1on, and when the armature 71 1s withdrawn from the plunger arm 61, since the spring 72 extends behind the pivot 77 of the arm 61, the said arm is necessarily rotated about the pivot 77 in a counter-clockwise direction (Fig. 5) by the spring 72, at which time the plunger 60 is carried into engagement with the bank springs. Now, after the plunger has been operated, if the release magnet 64 energizes, the armature 69 is attracted, and since the plunger 60 is prevented from further entering into the bank, the tension is restored in the spring 72 by the raising ofthe armature 71, and consequently by the raising of the link 73., 1t will line relay 123, it the called line is busy, as.: follows: The said relay 123, upon ener, 1,fizing` energizes the private magnet 129, as previously described, which latter in turn presses the springs 219 and 220 into contact. 14s soon as the said springs 219 and 220 engage, the release magnet 134 is placed in connection with the private wiper 137 (since the side switch wiper 132 is now in second position), which wiper 137 has been previously rotated onto a grounded contact. its a result a iow o1 current is sent through the release magnet 134 from the grounded private wiper 137 to the side switch wiper 132, to the private magnet springs 220 and'219, to the release magnet 134, did'erential relay springs 192 and 193, thence to the battery lead 144, and through battery B and to.

ground G. The release magnet 134, upon energizing, releases the connector switchshaft and restores the connector side switchto its hrst position, returnin the vertical magnet 127 to the control o1 t e vertical relay 122. Therefore, il the calling subscriber (Fig. 1) presses the signaling button 23 and grounds the vertical line conductor '120 he operates the vertical line relay 122, which latter in turn operates the Vertical' magnet 127. .The vertical magnet armature raises the switch-shaft, so that the normal post arm 221 permits the switch-shalt spring 222 to come into contact with the spring 223, and the busy-signaling current is sent to thecalling subscribers station. l1he calling subscriber, upon hearing the busy-signal, will understand that the desired line is in service, and will release the switching apparatus by hanging up his receiver'. The verticaland rotary line conductors 120 and 121 are again grounded simultaneously over circuits that have been explained, whereby the vertical and rotary lline relays 122 and 123 ot the connecter, together with the diflerential relay 126, are energized at the same time. The circuits for energizing said relays have already been pointed out. 1t

will be evident then that the line relays 122 and 123 will carry the release springs 218 and 212 into engagement at the same time that the differential relay 126 carries the differential relay springs 193 and 192 into engagement, setting up, therefore, the energizing circuit for the release magnet 1341 in series with the back-release relay 52 of the selector D, as already explained. As a result the connector is released and the release magnet 51 ot the selector D is energized, which in turn energizes the release magnet ba of the switch C. rEhe energized relays and magnets, ot course, remain so until the ground connectionsto the line conductors 120 and '121 are broken, at which time the switches become fully restored,` as has already been explained. 1n the master switch E special provision is made in the diierential relay 97 whereby the said relay may become energized by either a positive or a negative guarding potential at the Contact points a. Suppose that the release magnet 51 remains energized for any reason at anyI time after the line switch C becomes trunlred to the selector D; then since the springs 217 and 218 are in engagement a grounded positive potential appears at the contact point 108-instead et a negative potential, as pref- Viously explained-by way olf the conductors 116 and 14:5o New, when the wiper 99 en gages the said contact point and the common i plate 98, the dii'ierential relay 97 beeomes energized over a circuit extending trom ground G12 through the springs 218 21'?, private conductor 116, conductor 11d-3, con tact p 108, wiper arm @gto the plate 98, conductor 14127, throng r 22-1 ,n .ihm fa' ae t c c.. erentia r v lni prises a heat-coil 55. The said heat-coil is included in a series circuit between the main battery and the lead that supplies current to all of the circuits ot the switch D. 11S for any reason the line becomes grounded and a circuit is established through the heat-coil which is maintained for a considerable length of time, said heat-coil blows, and the star-wheel part et the vheat-coil, becoming unsoldered, revolves and permits the springs 225. and 226'vto come into contact, and the springs 160 and 159 to separate, the latter two breaking the battery lead circuit at the' energizes the release magnet 61 of the switchy C. The .said relays and magnets all remain energized until the heat-coil 55 blows. lll/hen the said coil blows, the relays d?" and t9 will,

oil course, denergize, since the connection to battery :tor the said relays is then brolren between the heat-coil springs 160 and 159. lWhen the said relays denergiae, the release magnet 51 denergizes also, and the release magnet 611 ofthe switch C denergizes as a result, thus restoring the switch. its soon as the cut-od3 relay 62 regains its normal position and closes the circuit througv trip magnet 63, the switch C will a air in and more onto the neat trunlr line o some other switch similar to the switch D, the heat-coil of which will in time be blown. IThis operation will occur with each trant: line until all the selector switches o1 group are put out et service. "W ith the rangement shown, however,

the doen ing of the release magnet 51 is not parmi 1 to produce the dener iaation ont the magnet or the switch @il the hea 55 is blown, because a permanent aus: energizing circuit is established throu release m @net 6&1 o 'f e heat l s j and 22d come -en the osition the indiv through either of said lamps.

exchange-that is, it may be made common to all the selector switches of the exchange, or to a part of the selectors, and is adapted to become energized in series with any release magnet 64 of any line switch C of the exchange or section to which it is allotted. Upon energizing, the said relay closes a local circuit by pressing the springs 227 and 228 into Contact, in which circuit is included the signal bell 229. The said circuit may be traced from ground G1 to the sprmgs 228 and 227, bell 229 to the ringer generator 230 and back to ground G16. The bell 229 is, of course, designed to call the switchboard attendants attention to the fact that some switch is in trouble in the exchange. Not only does the said relay energize to give an audible signal, but the lamp 56 (which is a group lamp) provides a visual signal-that is, the said lamp is adapted to light whenever any one of the switches allotted to the group of individual switches to which the individual switch C belongs is put out of service. rlFhe relay 57 may be allotted to only a part of the exchange if desired. As

indicated in Fig, the lamp 56 may be considered as belonging to one group of selectors, the lamp 56 to another group of selectors, and the lamp 562 to another group ot selectors, while the relay 57 is adapted to energize whenever a circuit is established lt is therefore evident that when the relay 57 energizes and delivers an audible signal, the attendants will see which light is burning and willv at once know in which sub-group the trouble may be found. @t course, trouble may be found in one of the groups or inall ot the groups, which tact will be indicated by the lamps. 4rlFhe attendant is, therefore, enabled to locate trouble quickly and remedy the cause. Hence it will be seen that when the heat-coil 55 blows and removes the battery connection from the switch D, if the re lease magnet 5l has energized, although the selector releases, the line switch C does not release, but remains on the trunlr line to pre vent the said line switch from causing trou ble on the other trunlr lines, and at the same time a signal is given to indicate the trouble. Referring to Fig. l, it will be understood that the lamp 56 is common to any subgroup of selectors, and that the lamp 562 is common to any sub-group ot selectors; but the heat-coils 55 and 552 are, of course,-in dividual to some one of the switches of their respective groups, said heatacoils being showni to simply indicate the circuits. 'lhe lamp 58, as shown, is adapted to light when any of the side switch wipers d5, 'l5' and 4:52, which belong to the selector switches of the same group, pass to third position, thus indicating at a glance if any of the selector switches have trunlred through to the next set or" switches. @ne terminal otsaid lamp rasante is permanently connected to battery while the said side switch wipers are all connected to ground. As shown in Fig. l, the heatcoils 235 and 236 are allotted to rst-selec tors of the group to which selector D'belongs, and any one of the said heat-coils.

blowing closes a circuit through the signal lamp `56 which is allotted to this particular group of first-selector switches.` As pre*- viously explained, the lamps 56 and 562 are individual to their respective groups in the same manner in which the lamp 56 is individual to its group. lt will be understood that locking a grounded individual switch onto a trunk line will maintain a guarding potential at the master switch bank contact corresponding to the seized trunk line, thus preventing any subscriber from plunging in onto the established connection. This method of automatically. supervising is especially adapted to an automatic district system, in which case the individual switches and the connectors will be located at sub-centrale, while the selector D will be located at the main exchange; and from the main exchange it will be possible to detect at once which switchesat the subcentrals are in trouble. Said sub-centrals may comprise a group of one hundred line switches and a percentage number ot con-V nectors, and at the main exchange there willI be provided a set ot selector switches tor each sub-central station. ln that case, it only first-selectors are used at the main ena, change lor trunlring purposes, the system' would be limited to a comparatively small number of sub-central oilices; but in castle that a larger system is desired additional" selectors may be added, as is well lrnown.

The relays and magnets may be wound to any suitable resistance, but with a central battery ot' nity volts good results have been obtained when the lamp relay 53 is wound to a resistance ont titty-hva hundred ohms, the differential windings 22d and il@ ot the relay 97 to litteen hundred ohms each, and the trip magnet 63 to a resistance ot six hundred ohms. l '.lhus it will be seen that the blowing o t the heat-coil when a subscribers line is ounded automatically releases the seiaed ust-selector without releasing the individual switch allotted to the grounded line.. When the attendant restores or resets the heat-coil, the individual switch will then he released, providing the abnormal ground at the subscribers station has in the meantime disappeared or been removed. onsequently, ll provide means for supervising the outlying individual switches :from the central station, making it possible to remedy various hind's ol' out ying trouble without the necessity ot sendin a trouble-man out of the exchange. lll' ith it e arrangement shown, the attendant at the central exchange can release the sublll@ les

llfl

llli

aaeacia scribers individual switch by simply pressing the armatures of the line relays l? and i9 of the seized first-selector.

`With further respect to the subscribers individual switch C, it will be seen that each plunger is adapted to occupy a trunk line without closing electrical connections between the same and the subscribers telephone line. ln other words, a subscriber may be occupying a certain trunk line without having his line connected therewith, and without using his telephone. ln such case the occupied or selected trunk line remains occupied until the last trunk line in the bank has been seized by some other subscriber; then the plunger which has been temporarily held in an intermediate or hallway position is caught by the dange on the shaft 9i as the latter returns to normal position or starting point, thus allowing the plunger to completely withdraw from the terminal of the trunk line which it was occupyingand to swing into line with all other plungers which are at that time in engagement with the shaft. Consequently, should a subscriber call and use a trunlr line, he may then call again and use the same trunk line, providing the shaft 9i has not in the meantime rotated to a position where it allowed the plunger to completely withdraw trom the terminal ot the trunlr line. llt a subscriber uses a trunh line tor some length ot time, and while he. is thus occupying it the shaft 9st ltravels to the end oit its forward f rotation, and then travels bach to normal position and starts over afrain, betere the subusing'the trunlr line, and the plunger occu-` pying the trunk line is liable to be piclred up by the motion of the shatt in either direction@ in any event, and as explained, each subscriber is always giron an opportunity to redll peat his call and thereby malte connection with the same trunlr line, thus increasing the speed and ediciency ot the service. linthis way two kinds ot idle plungers are possible, to-wit, plungers which are lined up on the shalt, and plungers which are scattered through the trunk. terminals and only partially withdrawn therefrom.

As to the district sustem, it will be seen that third trunk conductors are, employed l between the central station and the sub-central stations, these third trunks being .used

by the subscribers lor effecting an automatic trunk release back lromthe connectors and through the selectors to the individual switches. These third trunks are also, as ein plained, adapted for use by the central station attendants for releasing or supervising the subscribers individual switches. Furthermore, with the lamp arrangement provided at the exchange and employed in combination with the third trunks, it is possible tor the central station attendants to su pervise or test the subscribers lines to ascertain their condition.

lVhat lclaim as my invention is l. ln a telephone exchange system wherein there is a release conductor separate trom the talking circuit, an automatic selector provided with :ined-normal lamp, a local circuit for said lamp, an oil-norinal or super `risory relay tor said selector, said relay controllingthe circuit ot said lamp, and a circuit including said release conductor tor energizing said relay.

2. ln a telephone exchange system, the combination of an automatic switch, a telephone line leading thereto, a suitable'heatcoil, means tor causing the heat-coil to operate when brought into coimection with the switch by an abnormal grounding oi the tele hone line, and means tor automati cally re easing the said switch when the heat coil is reset or restored to normal condition.

3. ln a telephone exchange system, the combination oit trunk lines, a non-numerical switch, means for operating said switch to select idle trunk lines, means lor releasing said switch from the trunlr lines, and tor causing said switch to occupy the trunl line after releasing therefrom, whereby a subscriber alter releasing may call again and get the same trunlr line.

d. ln a telephone exchange system, the combination ot' trunlrs, a subscriberls individual switch for selecting' idle trunlrs, means tor ilully releasing said switch trom Lselected trunk, and means for temporarily preventing a full release trom a selected trunk, and for thereby retaining the'selection ot thetr'unlr by a partial release ot said switch.

5. ln a telephone exchange system, the combination or trunkl lines, an automatic trunk-selecting switch mechanism having provisions lor first edecting a partial release trom a selected trunlr line, Jlor thereby temporarily occupying the trunlr and permits ting the subscriber to call again and get the saine trunk line, and means by which a partial release trom a selected trunlr is atterward made complete.

t. ln a telephone exchange system, the

idle trunlr is selected iler the nent cal lil@ ,rie

subscriber, having provisions for elil'ecting only a partial release from a trunk when the subscriber is through using the same for completing the release it the trunk line thus temporarily operated is necessary for use by another calling subscriber, whereby each calling subscriber after releasing may call again and get the same trunk line, providing the latter has not in the meantime been combination of trunks, subscriber-controlled automatic means tor selecting idle trunks, means by which a subscriber may'disconnect from the trunk which he was using without discontinuing the occupancy or seizure thereof, means by which a second subscriber may discontinue the occupancy or seizure ol the said trunk, and means by which a third subscriber may bring the said completel released trunk into service for tal 'ng purposes.

9. ln a tele hone exchange system, the'A combination o a plurality yot trunks,- auto'- matic means by which a subscriber alter using a trunk may temporarily occupy the same after disconnecting therefrom, automatic means whereby another subscriber may call'and seize the idle trunk thus ternk porarily occupied by the tirst subscriber, and automatic means by which the second subscriber also selects another idle trunk tor the lirst subscriber.

10. ln a telephone exchange system, the combination ot a plurality ot trunks or com mon talking connections, a plurality ot telephone lines said trunks. being less in number than the te ephone lines, means tor connecting the'telephone lines with reselected idle trunks, means by which the isconnection ot a calling telephone line from a seized trunk tem Aorarily retains the said line in selective rela ion to said trunk, and automatic means by which another calling tele hone line may destroy the said selective re ation between the said telephone line and its preselected idle trunk.

il. ln a telephone exchange system, the

combination. ot telephone lines, a bank ot v, trunk line terminals tor each telephone line,

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a Swingin and endwise-movable' plunger for each telep one line, each plunger adapted to enter its allotted bank ot terminals to close connection with an idle trunky line, a shaft rovided With means tor enga g and se` ectively operating all ot saidA piangere,

nana-ara means individual to the diderent telephone lines for causing the plungers to enter selected terminals in the banks, and' common means by which said shaft is actuated each time an idle trunk line terminal is seized by a calling telephone line, each plunger provided wlth a broad portion havin a notch at the center thereof, and said shaft providedl with a flange adapted to engage the notches in the plungers, each plunger provided with a finger adapted to remain in the selected trunk line terminal to prevent movement ot the plunger before the shaft rotates sum.- cient y to bring its Iflange into engagement with the notch on the other end of such plunger. Y

12. ln a telephone exchangesystem, a plurality of trunk lines, a plurality ot trunking switches each provided with a swinging and endwise-movable plunger, a bank of trunk line terminals for each plunger, means in,- cluding a master switch 'for causing said plungers to select idle trunk lines, means by which the plungers are retained in engagement with the banks when disconnections aremade from trunk lines', and means tor causing full withdrawal ofthe plungers by a subsequent operation ot the master switch.

13. lln a telephone system, a line, a swinging and endwise-movable plunger individual to said line, a bank ot contacts to which the plunger is allotted, said plunger provided with an enlarged portion having a notch therein, a movable member provided with a `Hange for engaging said notch to swing the plunger relatively to said bankotcontacts, means for causing the plunger to enter the said bank of contacts, controllable over the line, means tor retaining said plunger in a partially restored or withdrawn position untltsubsequent actuation ot said movable member brings said lange into position to engage the said notch, and lines leading trom said bank.

la. ln a telephone exchange system, the combination ot a plurality of trunk lines, a

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plurality ot telephone lines, automatic means tor closing enmnection between a calling tele- I' phone line and a preselected idle trunk line,

means for disconnecting the calling tele-` phone line from the seized trunk line, and

tor retaining the disconnected telephone line in selective relation tothe trunk line with which it was connected to permit the line to call again and get the same trunk line, vand means by which another telephone line may connect with the said preselected idle trunk line.

15. .lint a telephone exchange system, the combination ot a plurality et trunk lines, means by which a calling subscriber connects with an idle trunk line., and means by which a .calling subscriber in releasing continues to occupy the disconnected trunk line to the-exclusion ot all other idle subscribers,

4itl. ln a telephone exchange system, an automatic selector provided with an odnormal lamp, a local circuit for said lamp, an oli-normal or supervisory relay for said selector, said relay controlling the circuit oil said lamp, an energizing circuit tor said relay including a trunk connection, and common battery connector switches, together with electrically controlled means lor supplying talking current through the said connector switches to the substations ot calling and called subscribers.

i7. ln a telephone exchange system, an automatic selector switch provided with first and second supervisory or oilnormal lamps, a circuit for lighting the first lamp during the initial operation ol the selector switch, a circuit for lighting the second lamp after the selector switch is through operating, and common battery connector switches, together with electrically controlled means for supplying talking current through the said connector switches to the substations `of calling andcalled subscribers.

18. ln a telephone exchange system, the combination of an automatic switch, a telephone line leading thereto, a suitable heatcoil, means for causing the heat-coil to oper- 'ate when brought into connection with the switch by an abnormal grounding of the telephone line, means for automatically releasing the said switch when the heat-coil is reset or restored to normal condition, and means including common battery connector switches for extending connection from said first-mentioned switches `to the called subscribers line, together with means for supplying talking current through the said connector switches to the substations of calling and called subscribers9 lines.

19. In a telephone exchange system, the combination of a first-selector, means for causing said selector to perform a trunking operation in accordance with the first digit of the called number, a visual signal for announcing the initial operation of said first., selector, a separate visual signal associated with said selector for announcin that the selector has completed its operation and is temporarily in an off-normal condition, and common battery connector switches, together with means for supplying talking current through the said connector switches to the substatio-ns of calling and called subscribers.

20. lin a telephone exchange system, the combination of trunk lines, an automatic 'trunk-selecting switch, means for indicating the initial operation of said switch, means associated with said switch for announcing the completion of the operation of the switch and the temporary seizure thereby of one ot said trunk lines, and common battery connector switches, together With means for supplying talking current through the said connector switches to the substations of calling and called subscribersn 2l. ln a telephone exchange system, an electrically-propelled and stepby-step actuated switch provided with a plurality or visual signals for indicating its initial and linal operations, and. common battery com ncctor switches, together with means for supplying talking current through the said connector switches to the substations ot' calling and called subscribers.

22. ln a telephone exchange system, the combination of trunk lines, means for selecting idle trunk lines, means :tor releasing from the trunk lines, means ttor occupying.

the trunk line after releasing therefrom, whereby a subscriber after releasing may call again and get the same trunk line, means including commen battery connector switches for eatencling connection from said trunlr lines to the called subscribers line, and means for supplying talking current through the said connector switches to the substa tions of calling and called subscribers.

23. lin a telephone exchange system, the combination ot' trunks, a subscribcrs individual switch for selecting idle trunks, means for fully releasing from a selected trunk, means for temporarily preventing a full release from a selected trunk, together with provisions for retaining the selection of the trunlt by a partial release therefrom, means including common battery connector switches for extending connection from said trunk lines to the called subscribers line, and means for supplying talking current through the said connector switches to the substations of calling and called subscribers.

2t. ln a telephone exchange system, the combination of trunk lines, an automatic trunk-selecting switch mechanism having provisions for first effecting a partial release from a selected trunk line, for thereby temporarily occupying the trunk and permitting the subscr1ber to call again and get the same trunk line, means by which a arl tial release from a selected trunk is atterward made complete, means including common battery connector switches for extending `connection from said trunk lines to the called subscribers line, and means for supplying talking current through the said connector switches to the substations of calling and called subscribers.

25. ln a telephoneexchange system, the combination of trunk lines, automatic means by which each calling subscriber is given a preselected trunk line and by which another idle trunk is selected for the next calling subscriber, having provisions for etfecting only a partial release from a trunk when the subscriber is through using the same, ior completing the release it the trunk line thus temporarily operated is necessary itor use by another calling subscriber, where- 'Mill lll@ 

